1. Field of the Invention
The invention is generally related to a method for forming magnetic, crosslinked chitosan support materials, and magnetic, crosslinked chitosan products obtained by this method.
2. Description of the Prior Art
The application of magnetic separation technologies to biotechnology has been proposed and practiced. E.g., see D. Melville et al., "Direct magnetic separation of red cells from whole blood", Nature, Vol. 255, Jun. 26, 1975, p. 706; C. Setchell, "Magnetic Separations in Biotechnology-A Review", J. Chem. Tech. Biotechnol., 1985, 35B, 175-182; and undated trade brochure by Paesel-Lorei GMBH & Co., "Magnetic Separation with Micro-Particles", Flinschstr. 67, W-6000 Frankfurt am Main 60.
As described in L. Nixon et al., "Preparation and Characterization of Novel Magnetite-Coated Ion-Exchange Particles", Chem. Mater., Vol. 4, No. 1, 1992, 4, 117-121. magnetizable particles for bioseparations have been made by incorporating magnetite into ion-exchange gel particles in two different modes. In one mode, the magnetite was deposited as a thin permeable layer on the surface of the ion-exchange beads, which were cross-linked agarose functionalized with carboxymethyl exchange groups or sulfopropyl groups (i.e., S-Sepharose), to form a coated type of magnetic particle. In a second mode, the magnetite was dispersed into agarose gel prior to bead formation.
R. H. Marchessault et al., Polymer, 33, 4024-4027 (1992), disclose a technique for preparing magnetic cellulose fibers and paper obtained by synthesizing ferrites in situ. In situ synthesis of iron oxide particles was performed by Marchessault et al. via careful oxidation of ferrous hydroxide precipitated with caustic from the ferrous ion-exchanged form of the matrix. The chemistry yielded magnetic fibers containing small ferrite (Fe.sub.3 O.sub.4) particles of about 10 nm in size. Marchessault et al. exemplify carboxymethylated cellulose fibers as the material subjected to the magnetization scheme disclosed therein, but also suggest that the process could be practiced with a wide range of natural biopolymers such as polysaccharides and lignocellulosics with amino, carboxyl and sulfonic acid groups, such as chitosan, although no reference nor distinction is made as between uncrosslinked and crosslinked forms thereof.
Chitosan is a generally known support material for separation processes. Chitosan is the acid-soluble deacetylation product of chitin. For example, chitosan is the product of alkaline hydrolysis of abundant chitin produced in the crab shelling industry. Chitosan, a biopolymer soluble in dilute (0.1 to 10%) solutions of carboxylic acids, such as acetic acid, is readily regenerated from solution by neutralization with alkali. In this manner, chitosan has been regenerated and reshaped in the form of films, fibers, and hydrogel beads. For instance, chitosan beads are prepared in one conventional method by precipitating dilute solutions of chitosan in acetic acid into alcoholic or aqueous sodium hydroxide followed by solvent exchange with water. However, in contrast to beads from cellulose, which are insoluble in most organic solvents, acids and bases, chitosan retains the solubility in dilute acids of the parent biopolymer. This solubility is typically overcome by inducing crosslinking. A conventional chitosan crosslinking reaction involves dialdehydes, such as glutaraldehyde, or diglycidyl ethers (such as butanediol diglycidyl ether, or epoxides like epichlorohydrin). Chitosan beads crosslinked with diglycidyl ethers are commercially available under the trade name CHITOPEARL, as manufactured by Fuji Spinning, Ltd., Japan.
Also, various researchers have discussed blending chitosan and cellulose to produce biodegradable films (see, for example, U.S. Pat. No. 5,306,550 to Nishiyama et al.; Hosokawa et al., Ind. Eng. Chem. Res., 29:800-805 (1990); Hasegawa et al., J. Appl. Polym. Sci., 45:1873-1879 (1992)). Though cellulose contains only trace amounts of carbonyl groups, these trace amounts of carbonyl groups are suspected in the art to play an important role in crosslinking to chitosan to form a crosslinked polymeric network of cellulose and chitosan.
Also, it has been demonstrated that complexes of chitosan with acetic acid (viz., chitosonium acetate) are converted to chitin (i.e., the N-acetylamide of chitosan) by a heat-catalyzed amidification or dehydration reaction, in U.S. Appln. Ser. No. 08/435,866 to Glasser et al., filed May 5, 1995. The amidification reaction described in U.S. Appln. Ser. No. 08/435,866 converts acid-soluble chitosan into acid-insoluble chitin.
However, because chitosan is easily solubilized and processed, a great deal of research in the hydrogel field has been devoted to experimentation with and/or use of chitosan in a wide variety of applications such as bioseparations. The art would be highly interested in a facile technique to form magnetic-functionalized, crosslinked chitosan support material.